Python: Refactor chat completion concept samples

[TaoChenOSU]

Motivation and Context

Our chat completion concept samples are not well organized and over-complicated with prompts and different settings.

Description

This PR refactors the samples such that they only capture the essential concepts to the chat completion services. This PR also adds sample usage for all supported chat completion services in Semantic Kernel Python.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[eavanvalkenburg]

Loving this, looks great! Only thing that I would like to see added is a simple_chatbot_with_kernel_function that uses a template for the system message, chat history and user input, something like You are a ... {{ chat_history }}{{ user_input }}